G
galactosemia
An inherited metabolic disorder caused by an enzyme deficiency and transmitted as a recessive trait; it results in the accumulation of the sugar galactose in the body. The disorder is manifested soon after birth by feeding problems and diarrhea. Galactose is accumulated principally in the liver of the newborn infant, where it may induce cirrhosis, and in the lens of the eye, where cataracts may develop. Low glucose levels cause sufficient hypoglycemia to affect the central nervous system with resulting mental retardation. These ill effects can be prevented by removing milk and all other foods containing galactose and lactose from the diet.
gangrene
gangrene, local death of body tissue. Dry gangrene, the most common form, follows a disturbance of the blood supply to the tissues, e.g., in diabetes, arteriosclerosis, thrombosis, or destruction of tissue by injury. A second type, moist gangrene, results from an invasion of toxin-producing bacteria that destroy tissue. Gangrene usually affects an arm or leg, but it may occur anywhere, e.g., pulmonary gangrene may follow an abscess of the lung. Treatment of gangrene includes rest and the administration of antibiotics if the gangrene is moist and bacterial invasion is present. Excision of the diseased portions of the body may be necessary and, in advanced involvement, amputation of the part. In gas gangrene, which results from the invasion of wounds by anaerobic bacteria, gas forms under the skin and a watery exudate is produced. Emergency treatment with penicillin and antitoxin is needed; without treatment, gas gangrene is invariably fatal.
Gaucher's disease
The rare genetic disease involving a deficiency of an enzyme, glucocerebrosidase, which normally breaks down certain body glycolipids (i.e., lipids (fats) that have a sugar molecule attached). There are three types of the disease. In all three types, the enzyme deficiency results in a buildup of the glycolipid glucocerebroside in the bone marrow, liver, and spleen, resulting in anemia and other blood disorders, bone pain and pathologic fractures, and enlarged liver and spleen. In Type II, the central nervous system is also affected. Patients are severely mentally retarded and have difficulty controlling their muscles. The disease progresses quickly from birth and usually is fatal by the age of two. In Type III disease, the course is chronic and central nervous system involvement begins later on. The symptoms are the same as those of Type II. Type I disease occurs most often in Ashkenazi Jews of Eastern European origin, Type III in people of Swedish origin.
There is no cure for Gaucher's disease, but in 1991 an enzyme replacement drug, Ceridase, was approved and allowed people with Type I disease (the most common) to live nearly normal lives. Ceridase was extracted from human placental tissue in very small amounts and the supply was limited. In 1994, a genetically engineered version of the drug (Cerezyme) was introduced. Both were developed as orphan drugs and were controversial because of their costliness.
giardiasis
An infection of the small intestine by a protozoan, Giardia lamblia. Giardia, which was named after Alfred M. Giard, a French biologist, is spread via the fecal-oral route, most commonly by eating food contaminated by the unwashed hands of an infected person or by drinking groundwater polluted by the feces of infected animals such as dogs and beavers (hence the nickname “beaver fever”). It attaches itself to the walls of the small intestine and there multiplies quickly. About two thirds of infected individuals develop no symptoms. Symptoms, when present, occur one to three days after infection and consist of diarrhea, flatulence, and abdominal cramps, often accompanied by weight loss. In some cases the infection becomes chronic. Giardiasis has traditionally been considered a tropical disease, but it is becoming more common in developed countries, especially among gay men and among groups of very young children in close contact with each other, as in day-care centers before toilet training and proper handwashing techniques have been mastered. Diagnosis is by direct microscopic examination of the stool or by testing for antibodies to the parasite. In most cases no treatment is necessary. The drugs metronidazole, tinidazole, and nitazoxanide are sometimes prescribed.
gigantism
gigantism, condition in which an animal or plant is far greater than normal in size. Plants are often deliberately bred to increase their size. However, among animals, gigantism is usually the result of hereditary and glandular disturbance. Among humans, gigantism is produced by an oversecretion of growth hormones by the acidophilic cells in the anterior lobe of the pituitary, causing excessive growth of all the tissues of the body. The metabolic rate is usually at least 20% above normal, which could be caused by an excess of the growth hormone alone, or oversecretion of the thyroid hormone in addition. Usually hyperglycemia (overactivity of the insulin-producing cells of the pancreas) is present. This condition eventually leads to degeneration of the islet cells, causing diabetes. Because of these metabolic abnormalities, the life expectancy of a giant is considerably less than normal. The treatment for gigantism is usually irradiation of the pituitary. The excessive height of the pituitary giant, which is defined at various levels above 7 ft (213 cm), is caused by excessive growth of the long bones. However, if the pituitary becomes overactive after growth is complete (marked by closure of the epiphyses of the long bones), the condition known as acromegaly results. Giants appear in the legends and folklore of many cultures.
gingivitis
inflammation of the gums. It may be acute, subacute, chronic, or recurrent. The gums usually become red, swollen, and spongy, and bleed easily. Chronic gingivitis is the usual form, resulting from irritating bacteria or debris, food impaction, or poor dental restoration. It can also accompany vitamin C deficiency or metabolic disturbances such as diabetes. If left untreated, it can lead to the more serious pyorrhea, with gum destruction and loosening of teeth. Trench mouth, an ulcerative infection of the gums and mouth, is sometimes referred to as a form of gingivitis.
glaucoma
ocular disorder characterized by pressure within the eyeball caused by an excessive amount of aqueous humor (the fluid substance filling the eyeball). This causes pressure against the optic nerve and compression of the blood vessels of the eye—the resulting impairment of vision ranges from slight abnormalities to total blindness. Chronic open-angle glaucoma is the result of impeded drainage of aqueous humor. In acute angle-closure glaucoma, the anterior chamber of the eye is shallower and the iris may obstruct the meshwork at the entrance of the canal of Schlemm. Although glaucoma is a leading cause of blindness in the United States, with timely treatment blindness is almost always avoided.
Chronic glaucoma begins gradually over a period of months or years, usually in patients over the age of 40. There are no symptoms in the early stages, and the condition can be detected only by measurement of the intraocular pressure. Such an examination is recommended every three years for all persons over the age of 20. As the disease progresses, often the only symptom is a gradual loss of peripheral vision. Chronic glaucoma can usually be controlled with eye drops or pills that increase the outflow or decrease the production of aqueous humor; laser treatment is also effective in the early stages. If treatment is continued throughout life, useful vision will be preserved in most cases; untreated individuals will gradually become blind.
Acute closed-angle glaucoma, which accounts for only 10% of the incidence of the disease, begins abruptly with severe pain and blurred vision. It is a medical emergency that causes permanent blindness in two to five days if left untreated. Surgery is usually necessary.
gonorrhea
common infectious disease caused by a bacterium (Neisseria gonorrhoeae), involving chiefly the mucous membranes of the genitourinary tract. It may occasionally spread to membranes in other parts of the body, especially those of the joints and the eyes. Since the principal mode of transmission is sexual contact, gonorrhea is classified as a sexually transmitted disease. Gonorrheal conjunctivitis was once a prominent cause of blindness in the newborn, the infection being transmitted during delivery. Routine use of silver nitrate solution in the eyes of every infant at birth has largely overcome this problem.
The usual site of infection in women is the cervix. From there it can spread to the uterus and fallopian tubes and cause pelvic inflammatory disease, ectopic pregnancy, or infertility. Other complications, in both sexes, include infection of the joints, heart valves, and brain. Women are often asymptomatic, but may have a vaginal discharge or burning sensation on urination; men may have a discharge from the penis and pain on urination. Examination of the discharge reveals the presence of the bacteria. In most cases, the disease can be cured by adequate treatment with a fluoroquinolone or cephalosporin antibiotic such as ciprofloxacin or ceftriaxone. Failure of treatment is usually due to resistant strains. Prior infection does not confer resistance and reinfection is common.
gooseflesh
gooseflesh, temporary rumpling of the skin into tiny bumps, also called goose bumps and goose pimples, and technically known as cutis ansirina. In response to cold or certain emotional states, such as fear or rage, the smooth muscles of the subsurface layer (dermis) of skin tend to contract, causing the skin to pucker and body hair to stand erect. In furred animals this can serve a dual purpose. Erection of the fur may make an animal seem larger than it actually is and act to frighten away a potential aggressor. Second, the erect fur traps a blanket of air close to the skin thus providing the organism with additional insulation against loss of body heat. In humans, this response would seem to be vestigial.
gout
The condition that manifests itself as recurrent attacks of acute arthritis, which may become chronic and deforming. It results from deposits of uric acid crystals in connective tissue or joints. The presence of increased uric acid (a breakdown product of DNA) in the body distinguishes gout from other forms of arthritis, although hyperuricemia alone, which often occurs in the complete absence of gout, is not thought to be the sole causative factor. About 95% of patients with this disorder are men, usually over 30. Gout is associated with obesity and a hereditary factor in some cases. Diet also has an affect on gout. Consumption of meat and seafood, which are high in purine (from which digestion produces uric acid), increase the risk of gout, and gout is worsened by kidney problems and drinking alcoholic beverages, which slow the excretion of uric acid. Beer, which is higher than other alcoholic beverages in purines, also has been shown to increase the risk of gout.
Gout usually begins with an acute attack of pain, inflammation, extreme tenderness, and redness in the affected joint—often the big toe and sometimes the ankle or knee. After repeated attacks the disease can cause the deposition of sodium urate crystals in the tissues about the joints, causing stiffness and deformity. The aim of treatment is to minimize the formation of uric acid crystals. A high liquid intake that increases daily urine output is usually recommended. An acute attack of gout is usually treated with nonsteroidal anti-inflammatory drugs, such as indomethecine or naproxen, or the corticosteroid prednisone. Colchicine, a preparation of the meadow saffron, used since 1763 for gout, is still used when symptoms are not controlled by other drugs.
Gulf War syndrome
Gulf War syndrome, popular name for a variety of ailments experienced by veterans after the Persian Gulf War. Symptoms reported include nausea, cramps, rashes, short-term memory loss, fatigue, difficulty in breathing, headaches, joint and muscle pain, and birth defects. Ailments have been reported by American, Canadian, Australian, and British veterans alike; in some cases spouses of veterans have reported similar symptoms. The mysterious syndrome has sparked debate between veteran's groups, Senate investigators, and the military over questions of accountability, treatment, and compensation. Hypothesized causes include parasites, biological and chemical warfare agents, prophylactic vaccines and medications given against biological and chemical warfare agents, fumes from oil well fires, and stress. In 1994 an advisory panel organized by the National Institutes of Health reported that the syndrome represented many illnesses and many causes; they deemed biological and chemical warfare agents unlikely as causes. Causes for the illnesses in many subsets of patients have been identified, e.g., some 30 veterans had leishmaniasis, a parasitic disease spread by sand flies, but in many instances the cause has not been identified. In 1999 researchers said that brain scans of some sick veterans revealed signs of damage caused by exposure to toxic chemicals. A study in 2004 suggested that some veterans may have been sensitive enough to otherwise low levels of poison gases to cause symptons associated with the syndrome. Some medical historians have pointed out that syndromes of undiagnosable diseases have occurred after other wars, including World Wars I and II and the American Civil War.